This invention relates to a combustion heater for use in automotive vehicles, and more particularly to a combustion heater of this kind which is excellent in fuel ignitability and durability of a glow plug thereof, and has reduced power consumption, and which can effect positive extinction.
A conventional combustion heater for automotive vehicles, which is used for heating the vehicle compartment or for keeping foods warm, is disclosed in Japanese Provisional Patent Publication (Kokai) No. 58-57065, which comprises a combustor equipped with a glow plug, a voltage-applying device for applying a voltage to the glow plug, a fuel feed pump for supplying fuel to the combustor, a blower for supplying air for combustion to the combustor, a sensor for detecting ignition within the combustor, and a control system for controlling the operations of the glow plug, the fuel feed pump, and the blower.
According to this known combustion heater for automotive vehicles, when a signal for starting ignition is supplied to the control system, a battery as the voltage-applying device applies a predetermined voltage to the glow plug for preheating, and after a predetermined time period for preheating has elapsed after the start of application of the predetermined voltage, the fuel feed pump and the blower start to operate in response to control signals from the control system for supplying fuel and air to the combustor.
However, the predetermined time period for preheating is set to such a long time period as to ensure ignition under any condition, taking into consideration the ambient temperature, the combustion chamber temperature, and variations in component parts of the heater, such as the glow plug and the fuel feed pump. Therefore, even when the inside of the combustion chamber is still hot immediately after extinction, preheating is carried out over the same time period as in the case where the combustion chamber temperature is low, which leads to wasteful consumption of electric power and a shortened life of the glow plug.
In a conventional combustion control system of the combustion heater, in general, upon extinction, i.e. when the heater is caused to cease burning, it is necessary to continue feeding the combustor with air after fuel supply is stopped until the remaining fuel in the wick, which is impregnated with fuel, burns out. Therefore, it has been proposed to feed the combustor with air at a predetermined constant flow rate after stoppage of fuel supply, by Japanese Provisional Utility Model Publication (Kokai) No. 58-15861. However, since the amount of remaining fuel in the wick progressively decreases and hence the amount of vaporized fuel progressively decreases after stoppage of fuel supply until complete extinction, the amount of air supply becomes excessive if the air is supplied at the predetermined constant flow rate, so that the air-fuel ratio in the combustor becomes lean, which leads to occurrence of pale blue smoke and hence emission of noxious gases, or to blowing-out of the fire before the remaining fuel burns out. Particularly when the fire is blown out before the remaining fuel burns out, white smoke of unburnt gases is produced from residual fuel contained in the wick immediately after the blowing-out of the fire, or the residual fuel is carbonized due to heat remaining in the heater and attached to the wick, resulting in a shortened life and degraded ignitability of the wick.
Further, once extinction of the heater is completed, scavenging has to be effected by continuing air supply in order to cool the heater and discharge gases produced by vaporization of fuel from the heater for safety purposes.